OUTLINE: This is a dose escalation study of pentoxifylline (PTX). Patients receive hydroxyurea (HU) and PTX IV continuously 5 days a week concurrently with cranial radiotherapy twice daily, 5 days a week, for 4 weeks in the absence of disease progression or unacceptable toxicity. The first cohort of 3 patients is treated with radiotherapy and HU alone. Subsequent cohorts of 3-6 patients receive HU and radiotherapy plus escalating doses of PTX until the maximum tolerated dose of PTX is determined or serum or CSF drug concentrations reach 0.4-2.0 mM in 6 consecutive patients with acceptable toxicity. The MTD is defined as the dose immediately preceding that at which 2 of 6 patients experience dose-limiting toxicity. Patients are followed at 1 week, at 1 and 3 months, every 3 months for 2 years, and then every 4 months for 5 years.